We assemble a sample of 24 hydrogen-poor super-luminous supernovae (SLSNe). Parameterizing the light curve shape through rise and decline timescales shows that the two are highly correlated. Magnetar-powered models can reproduce the correlation, with the diversity in rise and decline rates driven by the diffusion timescale. Circumstellar interaction models can exhibit a similar rise-decline relation, but only for a narrow range of densities, which may be problematic for these models. We find that SLSNe are approximately 3.5 magnitudes brighter and have light curves 3 times broader than SNe Ibc, but that the intrinsic shapes are similar. There are a number of SLSNe with particularly broad light curves, possibly indicating two progenitor channels, but statistical tests do not cleanly separate two populations. The general spectral evolution is also presented. Velocities measured from Fe II are similar for SLSNe and SNe Ibc, suggesting that diffusion time differences are dominated by mass or opacity. Flat velocity evolution in most SLSNe suggests a dense shell of ejecta. If opacities in SLSNe are similar to other SNe Ibc, the average ejected mass is higher by a factor 2-3. Assuming κ = 0.1 cm 2 g −1 , we estimate a mean (median) SLSN ejecta mass of 10 M (6 M ), with a range of 3-30 M . Doubling the assumed opacity brings the masses closer to normal SNe Ibc, but with a high-mass tail. The most probable mechanism for generating SLSNe seems to be the core-collapse of a very massive hydrogen-poor star, forming a millisecond magnetar.

Context. The Public European Southern Observatory Spectroscopic Survey of Transient Objects (PESSTO) began as a public spectroscopic survey in April 2012. PESSTO classifies transients from publicly available sources and wide-field surveys, and selects science targets for detailed spectroscopic and photometric follow-up. PESSTO runs for nine months of the year, January -April and August -December inclusive, and typically has allocations of 10 nights per month. Aims. We describe the data reduction strategy and data products that are publicly available through the ESO archive as the Spectroscopic Survey data release 1 (SSDR1). Methods. PESSTO uses the New Technology Telescope with the instruments EFOSC2 and SOFI to provide optical and NIR spectroscopy and imaging. We target supernovae and optical transients brighter than 20.5 m for classification. Science targets are selected for follow-up based on the PESSTO science goal of extending knowledge of the extremes of the supernova population. We use standard EFOSC2 set-ups providing spectra with resolutions of 13-18 Å between 3345−9995 Å. A subset of the brighter science targets are selected for SOFI spectroscopy with the blue and red grisms (0.935−2.53 μm and resolutions 23−33 Å) and imaging with broadband JHK s filters.Results. This first data release (SSDR1) contains flux calibrated spectra from the first year (April 2012(April -2013. A total of 221 confirmed supernovae were classified, and we released calibrated optical spectra and classifications publicly within 24 h of the data being taken (via WISeREP). The data in SSDR1 replace those released spectra. They have more reliable and quantifiable flux calibrations, correction for telluric absorption, and are made available in standard ESO Phase 3 formats. We estimate the absolute accuracy of the flux calibrations for EFOSC2 across the whole survey in SSDR1 to be typically ∼15%, although a number of spectra will have less reliable absolute flux calibration because of weather and slit losses. Acquisition images for each spectrum are available which, in principle, can allow the user to refine the absolute flux calibration. The standard NIR reduction process does not produce high accuracy absolute spectrophotometry but synthetic photometry with accompanying JHK s imaging can improve this. Whenever possible, reduced SOFI images are provided to allow this. Conclusions. Future data releases will focus on improving the automated flux calibration of the data products. The rapid turnaround between discovery and classification and access to reliable pipeline processed data products has allowed early science papers in the first few months of the survey.

We present the results of optical, near-infrared, and mid-infrared observations of M101 OT2015-1 (PSN J14021678+5426205), a luminous red transient in the Pinwheel galaxy (M101), spanning a total of 16 years. The light curve showed two distinct peaks with absolute magnitudes, on 2014 November 11 and 2015 February 17, respectively. The spectral energy distributions during the second maximum show a cool outburst temperature of »3700 K and low expansion velocities (»-300 kms −1 ) for the H I, Ca II, Ba II, and K I lines. From archival data spanning 15-8 years before the outburst, we find a single source consistent with the optically discovered transient, which we attribute to being the progenitor; it has properties consistent with being an F-type yellow supergiant with L∼8.7´10 4 L e , » T 7000 eff K, and an estimated mass of =  M1 18 1 M e . This star has likely just finished the H-burning phase in the core, started expanding, and is now crossing the Hertzsprung gap. Based on the combination of observed properties, we argue that the progenitor is a binary system, with the more evolved system overfilling the Roche lobe. Comparison with binary evolution models suggests that the outburst was an extremely rare phenomenon, likely associated with the ejection of the common envelope of a massive star. The initial mass of the primary fills the gap between the merger candidates V838 Mon (5−10 M e ) and NGC4490-OT(30 M e ).

Super-luminous supernovae (SLSNe) of type Ic have a tendency to occur in faint host galaxies which are likely to have low mass and low metallicity. PTF12dam is one of the closest and best studied super-luminous explosions that has a broad and slowly fading lightcurve similar to SN 2007bi. Here we present new photometry and spectroscopy for PTF12dam from 200-500 days (rest-frame) after peak and a detailed analysis of the host galaxy (SDSS J142446.21+461348.6 at z = 0.107). Using deep templates and image subtraction we show that the lightcurve can be fit with a magnetar model if escape of high-energy gamma rays is taken into account. The full bolometric lightcurve from −53 to +399 days (with respect to peak) cannot be fit satisfactorily with the pair-instability models. An alternative model of interaction with a dense CSM produces a good fit to the data although this requires a very large mass (∼ 13 M ) of hydrogen free CSM. The host galaxy is a compact dwarf (physical size ∼ 1.9 kpc) and with M g = −19.33 ± 0.10, it is the brightest nearby SLSN Ic host discovered so far. The host is a low mass system (2.8 × 10 8 M ) with a star-formation rate (5.0 M yr −1 ), which implies a very high specific star-formation rate (17.9 Gyr −1 ). The remarkably strong nebular emission provide detections of the [O iii] λ4363 and [O ii] λλ7320, 7330 auroral lines and an accurate oxygen abundance of 12 + log (O/H) = 8.05 ± 0.09. We show here that they are at the extreme end of the metallicity distribution of dwarf galaxies and propose that low metallicity is a requirement to produce these rare and peculiar supernovae.

Supernova (SN) 2015bh (or SNhunt275) was discovered in NGC 2770 on 2015 February with an absolute magnitude of M r ∼ −13.4 mag, and was initially classified as a SN impostor. Here we present the photometric and spectroscopic evolution of SN 2015bh from discovery to late phases (∼ 1 yr after). In addition, we inspect archival images of the host galaxy up to ∼ 21 yr before discovery, finding a burst ∼ 1 yr before discovery, and further signatures of stellar instability until late 2014. Later on, the luminosity of the transient slowly increases, and a broad light curve peak is reached after about three months. We propose that the transient discovered in early 2015 could be a core-collapse SN explosion. The pre-SN luminosity variability history, the long-lasting rise and faintness first light curve peak suggests that the progenitor was a very massive, unstable and blue star, which exploded as a faint SN because of severe fallback of material. Later on, the object experiences a sudden brightening of 3 mag, which results from the interaction of the SN ejecta with circumstellar material formed through repeated past mass-loss events. Spectroscopic signatures of interaction are however visible at all epochs. A similar chain of events was previously proposed for the similar interacting SN 2009ip.